Certain embodiments of the present invention are directed to integrated circuits. More particularly, some embodiments of the invention provide systems and methods for current regulation. Merely by way of example, some embodiments of the invention have been applied to light-emitting-diode lighting systems. But it would be recognized that the invention has a much broader range of applicability.
Light emitting diodes (LEDs) are widely used for lighting applications. FIG. 1 is a simplified diagram showing a conventional LED lighting system. The LED lighting system 100 includes a controller 102, resistors 108, 116, 122, 124 and 128, capacitors 106, 110, 112 and 130, a full-wave rectifying component 104, diodes 114 and 118, an inductive component 126 (e.g., an inductor), and a Zener diode 120. The controller 102 includes terminals (e.g., pins) 138, 140, 142, 144, 146 and 148.
An alternate-current (AC) input voltage 150 is applied to the system 100. The rectifying component 104 outputs a bulk voltage 152 (e.g., a rectified voltage no smaller than 0 V) associated with the AC input voltage 150. The capacitor 112 (e.g., C3) is charged in response to the bulk voltage 152 through the resistor 108 (e.g., R1), and a voltage 154 is provided to the controller 102 at the terminal 148 (e.g., terminal VDD). If the voltage 154 is larger than a threshold voltage (e.g., an under-voltage lock-out threshold) in magnitude, the controller 102 begins to operate, and a voltage associated with the terminal 148 (e.g., terminal VDD) is clamped to a predetermined voltage. The terminal 138 (e.g., terminal DRAIN) is connected to a drain terminal of an internal power switch. The controller 102 outputs a drive signal (e.g., a pulse-width-modulation signal) with a certain frequency and a certain duty cycle to close (e.g., turn on) or open (e.g., turn off) the internal power switch so that the system 100 operates normally.
If the internal power switch is closed (e.g., being turned on), the controller 102 detects the current flowing through one or more LEDs 132 through the resistor 122 (e.g., R2). Specifically, a voltage 156 on the resistor 122 (e.g., R2) is passed through the terminal 144 (e.g., terminal CS) to the controller 102 for signal processing during different switching periods associated with the internal power switch. When the internal power switch is opened (e.g., being turned off) during each switching period is affected by peak magnitudes of the voltage 156 on the resistor 122 (e.g., R2).
The inductive component 126 is connected with the resistors 124 and 128 which generate a voltage 158. The controller 102 receives the voltage 158 through the terminal 142 (e.g., terminal FB) for detection of a demagnetization process of the inductive component 126 to determine when the internal power switch is closed (e.g., being turned on). The capacitor 110 (e.g., C2) is connected to the terminal 140 (e.g., terminal COMP) which is associated with an internal error amplifier. The capacitor 130 (e.g., C4) is configured to maintain an output voltage 158 to keep stable current output for the one or more LEDs 132. A power supply network including the resistor 116 (e.g., R5), the diode 118 (e.g., D2) and the Zener diode 120 (e.g., ZD1) provides power supply to the controller 102.
The LED lighting system 100 has some disadvantages. For example, the system 100 includes many components which may make it difficult to reduce bill of materials count (BOM) and achieve circuit minimization and may cause a long start up time due to large current consumption.
Hence it is highly desirable to improve the techniques of current regulation in LED lighting systems.